1. Field of the Present Invention
The present invention relates to a polyethylene terephthalate resin, and more particularly, to a polyethylene terephthalate resin containing a small amount of blue dye and inorganic particles and synthesized by using an inorganic Ti—Mg catalyst as a polycondensation catalyst.
2. Description of Prior Art
A conventional process for producing polyethylene terephthalate (PET) is to react purified terephthalic acid (TA) and ethylene glycol (EG) by a direct esterification reaction to yield bis(2-hydroxyethyl) terephthalate (i.e., monomer) and oligomers and water. This reaction is reversible and thus can be carried to completion by removing the water during the direct esterification process. The direct esterification process does not require a catalyst and conventionally no catalyst is employed.
The monomer then undergoes a polycondensation process to form PET. The polycondensation process typically uses antimony as a polycondensation catalyst. If necessary, a solid-state polymerization process may optionally follow the polycondensation process to increase the molecular weight of the resultant PET resins.
Recently, PET bottles have dominated over in drink-packaging applications and have almost replaced all kinds of glass bottles and aluminum cans. However, trace migration of antimony (Sb) from a PET bottle is capable of migrating into the drink contained therein, and it has been proven that the heavy metal, e.g. antimony (Sb), has seriously threatened to human health.
For solving this problem mentioned above, the process for producing polyethylene terephthalate (PET) have been taught to use an organic titanium-containing catalyst to replace the antimony (Sb) catalyst as a polycondensation catalyst during the polycondensation process to form the PET. However, to take the titanium-containing catalyst used as a polycondensation catalyst still has some defects which include the finished PET looks yellowish and susceptible to thermal degradation resulted in disadvantageously bringing relatively high concentration of acetaldehyde and cyclic oligomer in the PET. Therein, the problem of the finished PET looking yellowish is difficult to remedy even by adding dyes during the polycondensation process of manufacturing PET.
For example, U.S. Pat. No. 5,922,828 employs an organic tetrabutyltitanate (also known as TBT) as a titanium-containing catalyst and employs bis(2,4-di-tert-butylphenyl) pentaerythritol diphosphite (commercially named as Anti-Oxidant AT-626) as a stabilizer to reduce acetaldehyde concentration in the synthesized polymer. Nevertheless, this prior art still fails to overcome the problem of the finished PET looking yellowish.
U.S. Pat. No. 6,013,756 uses an organic tetrabutyl titanate compound as a titanium-containing catalyst during the polycondensation process of manufacturing PET and utilizes by addition of cobalt acetate to eliminate the defective yellowish appearance of the PET.
The embodiments disclosed in U.S. Pat. No. 6,500,915 also involves in using tetrabutyltitanate (TBT), phosphide and magnesium acetate to synthesize PET. However, this prior art provides no solution for elimination of the defective yellowish appearance of PET synthesized in the presence of the titanium-containing catalyst.
U.S. Pat. No. 6,593,447 has disclosed a polycondensation catalyst. For making the polycondensation catalyst organic titanium and phosphorous compounds are mixed in a certain proportion and dissolved in glycol to prepare a catalyst solution. The catalyst solution then reacts with anhydride under 200° C. to produce the polycondensation catalyst. However, this prior art provides no solution for elimination of the defective yellowish appearance of PET synthesized in the presence of titanium-containing catalyst.
U.S. Pat. No. 6,667,383 relates to PET synthesized in the presence of tetrabutyltitanate (TBT), phosphate esters and magnesium compounds. Yet, this prior art provides no solution for elimination of the defective yellowish appearance of PET synthesized in the presence of titanium-containing catalyst.
U.S. Pat. Nos. 6,489,433 and 6,541,598 respectively employ organic tetrabutyltitanate (TBT) or organic tetraisopropyl titanate as the polycondensation catalyst and additionally use a phosphonate ester to synthesize PET with desired color.
U.S. Pat. Nos. 7,094,863 and 7,129,317 use organic titanium diisopropoxide bis(acetyl-acetonate) or organic tetrabutyltitanate (TBT) as the polycondensation catalyst to synthesize PET. Bottle preforms made thereof provides with specific features of being bright and highly transparent and having low concentration of metal elements therein. Hot-filling bottles formed from such bottle preforms still maintain excellent transparency and desired dimensional stability at a filling temperature ranging from 195 to 205° F.
U.S. Pat. No. 6,451,959 teaches a solid titanium compound T that is prepared by hydrolyzing a titanium halide to obtain a hydrolyzate and then dehydro-drying the hydrolyzate. According to the cited prior art, the solid titanium compound T may be combined with other compounds E, such as Be-hydroxide, Mg-hydroxide, Ca-hydroxide, Sr-hydroxide or Ba-hydroxide. Therein, E/Ti molar ratio is between 1/50 and 50/1 while OH/Ti molar ratio is between 0.09 and 4.
U.S. Pat. No. 7,300,998 relates to a polycondensation catalyst applicable to synthesis of PET used for making bottles. Therein, Mg(OH)2 and TiCl4 are mixed in water to form an aqueous solution. Ammonia water is then added therein drop by drop to adjust the aqueous solution to about pH 9. Successively, an aqueous acetic acid solution is added therein drop by drop to adjust the aqueous solution to about pH 5. After filtering, washing and dissolving in ethylene glycol, the solution is treated by a centrifuge to have solid therein separated. The solid is then dried in vacuum at 40° C. for 20 hours before being ground into powders sized between 10 and 20 μm. The powders are afterward mixed with an ethylene glycol solution containing sodium hydroxide so as to obtain the polycondensation catalyst for use in synthesis of PET bottles. By using the sodium hydroxide, the cited prior art provides a polyester having high solid-state polycondensation rate and low concentration of regenerated acetaldehyde. However, this prior art provides no solution for elimination of the defective yellowish appearance of PET synthesized in the presence of titanium-containing catalyst.
Another known prior art is also to take a novel titanium-containing catalyst used as a polycondensation catalyst, while the titanium-containing catalyst is produced by reacting an aqueous MgCl2 solution with an aqueous NaOH solution at 170° C. for 30 minutes approximately, and the reacted solution is then filtered and washed to form an aqueous Mg(OH)2 slurry. On the other hand, an aqueous TiCl4 solution and an aqueous NaOH solution are mixed before being added into the Mg(OH)2 slurry. After the mixed aqueous TiCl4 and NaOH solution added drop by drop into the Mg(OH)2 slurry, the mixture is stirred for one hour for aging until TiO2 embraces on the outer surface of Mg(OH)2 in the slurry. Afterward, the slurry is filtered and washed to get solid part therein. The solid is dried and pulverized into powders that are later mixed with ethylene glycol to form a solution for use in polycondensation. As a result, both the reaction rate of the titanium-containing catalyst and the color of the polyester synthesized in the presence of the titanium-containing catalyst are similar to those of Antimony trioxide (Sb2O3).
In addition to the prior arts mentioned above, bottle preforms if made of PET synthesized in the presence of titanium catalysts and before capable of being blown into finished bottles require longer extended aging time than that of the bottle preforms if made of PET synthesized in the presence of antimony catalysts, otherwise, the bottle preforms synthesized in the presence of titanium catalysts if insufficient extended aging time will be inferior in dimensional stability and susceptible to shrinkage and deformation. In addition, insufficient extended aging time results in relatively low cyrstallinity of hot filled bottles made from heat-setted process, and accounts for relatively low hot filled temperature of filled bottles produced in the presence of titanium catalysts compared to filled bottles produced in the presence of antimony catalysts.